In an ore mine, passages called "passes" or "raises" normally extend between different levels of the mine and act as conduits for material that is to be conveyed from an upper level to a lower level by gravity. For example, ore mined at upper levels of the mine may travel down an "ore pass" to a crusher at a lower level.
Over a period of time, ore tumbling down the pass causes the wall of the pass to deteriorate. Chunks of waste material break off from the wall and fall down the pass. This is referred to as "sloughing". Where large chunks of material break away from the wall of a pass, they can even block or damage the crusher and interupt production of the mine. Sloughing can eventually lead to collapse of the pass. Seismic activity can also have a destructive effect on the condition of a pass.
For all of these reasons, it would be desirable to be able to monitor the condition of the wall of the pass from time to time. However, the passes are generally inaccessible and cannot be visually inspected. Attempts have been made to determine the contour of a pass (and thereby assess its condition) by drilling into the pass from adjacent mine shafts at several locations and measuring the depth of material through which the drill has cut at each location. However, such techniques are extremely expensive and unreliable. As far as is known, the technology to accurately determine the contour or profile of a pass has not been developed.
An object of the present invention is therefore to provide a method and apparatus for determining the profile of a subterranean passage such as an ore or waste material pass in a mine.